I'm not a professional tubaist, but I slept at Holiday Inn Express last night.......
Anyway, I played the three valve version of this horn at the Kanstul factory /showroom in Anaheim last week. (All of the four valve 5/4 horns were at the NAMM show that weekend.) I also played the four valve 3/4 BBb horn, the euphs and a bass 'bone. I used a Sidey SSH on the tubas and a Bach 3G on the "bone and euphs.
I'm a semi-pro (ooh, another label category?) quintet, German band, show and orchestra player, using a Miraphone 186 and a Yamaha YBB-621, both in BBb, and an old Olds Shooting Star (George Roberts) bass trombone.
Personally, I wasn't that impressed with the 5/4 horn's sound, although I did think the horn was really well made, (the braces fall into the "now why didn't anyone think of that before?" file.) The horn has a relatively open wrap and I wondered why they didn't go with a more compact design. (The horn takes up more room than it should.) I thought it was lacking in the tone department, nowhere near as rich a sound as my 186. Range was good, though, and you can pop the really low notes.
The 3/4 horn was much better, in my opinion. Good tone and resonance and a handy package. The valves were very good on this horn, too. Neither horn was uncomfortable to play, ergonomically speaking, but I think they would sell better with an ergo valve set. (That seems to be a direction that some mfr's are going.)
I understand from one of the trumpet players in my quint that the Kanstul piccolo trumpet is one of THE pic's to have. And they are doing a lot of nice work with red brass bells on trumpets, fluegs and 'bones. I understand that they just completed a double french horn. I just think that they still have some refinement to do on their big horns. It's nice to have another American company making horns and I think their ship is on the horizon.
If you are in the area I would suggest making arrangements to go by and play their horns. They are very friendly and accomodating. (the day I was there all of the sales staff were gone to the NAMM show and one of the factory guys let me into the showroom. He was very knowledgable and obviously enjoys making these horns.)